(1) Field of the Invention
The present invention relates to a surface modifying composition for vulcanized rubber and a method of modifying a surface of vulcanized rubber. More particularly, the invention relates to a non-solvent type surface modifying composition for vulcanized rubber in which a halogen-releasable halogenoid and an inorganic filler are uniformly dispersed in a waxy substance, and a method of modifying only a surface portion of the vulcanized rubber with such a composition without a polar solvent.
(2) Description of the Prior Art
As an adhesion technique for vulcanized rubber, there has hitherto been known a method wherein a solution of an unvulcanized rubber dissolved in an organic solvent such as toluene or a so-called rubber cement is applied to the surface of the vulcanized rubber and dried and thereafter an unvulcanized rubber is piled thereon to perform press vulcanization. In this method, however, a mold meeting with the requirements for one-piece molding must be manufactured every the molding and a complicated mechanical equipment for pressurization and heating is required. In addition, rubber to be adhered is limited to the same kind of unvulcanized rubbers as vulcanized rubber.
There is also known another method in which vulcanized rubber is adhered to the other material by using a polychloroprene (CR) in unvulcanized state, an acrylonitrilebutadiene copolymer generally called as nitrile rubber, a graft copolymer rubber produced by graft polymerization of the above rubber with vinyl compound such as methylmethacrylate or the like, or a rubber cement produced by dissolving a blend of the above rubber and phenol resin into an organic solvent. But, satisfactory adhesive force cannot yet be obtained by such a method. There is a still further method of using an air curing rubber cement in which the vulcanization is carried out by using an ultrarapid-accelerator or sulfur chloride. In this method, however, it is extremely difficult to obtain sufficient adhesive force.
As a method of treating a surface of vulcanized rubber, there has hitherto been performed a method in which the surface of the vulcanized rubber is strongly oxidized with a treating agent such as concentrated sulfuric acid, potassium permanganate, potassium dichromate or the like and then washed with water to remove the treating agent, and thereafter the thus treated vulcanized rubber is bent to produce fine cracks onto its whole surface, which is coated with an adhesive and is adhered to the other material. In this case, great care should be taken on the handling of the strong acid or strong oxidizing agent. Moreover, the adhesive force is insufficient and the use of such a strong oxidizing agent unfavorably degrades the vicinity of the vulcanized rubber surface.
In order to eliminate such defects, there has been developed a technique described in Japanese Patent Application Publication No. Sho 52-36,910, that is, a technique of treating the surface of the vulcanized rubber with a solution of a compound containing N,N-dihalosulfonamide group as a halogen-releasable halogenoid, whereby the vulcanized rubber can be adhered to a material of other kinds and the adhesive force is conspicuously improved.
However, this technique has still the following three drawbacks and is not widely applied for the industrial purpose.
(1) Since the organic solvent having a relatively high toxicity such as acetone, tetrahydrofuran is used, the technique cannot be applied to a place having no local ventilation apparatus.
(2) Since the halogen-releasable halogenoid is degrade to lose its effectiveness in a solvent having an active hydrogen in a relatively short time, once a solution of the halogenoid is prepared, it must be used usually in a half day, and within a day at the latest. Further, since the halogenoid dislikes water and degrades with water in air, extremely careful attention must be paid on the reserve of the halogenoid.
(3) Since the halogenoid is used in a form of solution, in surface modifying operation, it penetrates into the interior portion of the vulcanized rubber and modifies the vulcanized rubber to a thickness of about 10-15 .mu.m as measured from the surface thereof. Such a modification is unfavorable from the standpoint of flex resistance, which reduces the flex resistance of the vulcanized rubber.
As previously mentioned, there are not yet developed satisfactory surface modifying agents for vulcanized rubber and method of modifying the surface of the vulcanized rubber.